[Map] Fix default values of Stimulus Map Controller

[Kocal]

Q	A
Bug fix?	yes
New feature?	no
Issues	Fix #2417
License	MIT

This issue happens at doCreateMap when we called ->fitBoundsToMarkers() instead of ->center(...).

The value center was supposed to be null, but since I forgot to configure the default value of this.centerValue to null, it automatically used {} as default value (https://stimulus.hotwired.dev/reference/values#getters) and it breaks the code.

This bug has been introduced in #2385.

[github-actions]

📊 Packages dist files size difference

ℹ️ No difference in dist packagesFiles.

[Kocal]

Should be better now, TIL Stimulus values' default value does not behave like Vue props' default value 😅

I reverted my changes and used this.has... instead, they correctly switch from false or true if they absent or not (html attributes are not rendered when their value is null).